DEM USGS Digital Elevation Model Export Options Dialog

If the file format does not support multiple-slice lattices, the Select Slices dialog appears.

This dialog appears when a lattice or image module is selected and the File | Save Data command is chosen.

Specify the type of units for the XY coordinates in the source grid from the Source grid limits are in drop-down list. Click the arrow to display the list. Possible selections are Radians, Feet, Meters, Arcseconds, and Degrees. The export units need to be the same as the map units. For example, if the map units are lat/long, and you choose Meters as the X unit code, then there will be no conversion. If the map is in lat/long, then you have to choose to export as lat/long. You put in what the units of the map are, not what you want the export file to be in.

Specify the type of units for the Z (vertical) coordinates in the source grid from the Source grid Z values are in drop-down list. Click the arrow to display the list. Possible selections are Feet or Meters. The export units need to be the same as the map units. For example, if the map units are lat/long, and you choose Meters as the X unit code, then there will be no conversion. If the map is in lat/long, then you have to choose to export as lat/long. You put in what the units of the map are, not what you want the export file to be in.

Specify the block type for the DEM image from the Block type drop-down list. Click the arrow to display the list.. Possible selections are 15-minute, 7-minute, and Other.

Part 2: Specifications

National Mapping Program

Technical Instructions

U.S. Department of the Interior

U.S. Geological Survey

National Mapping Division

Appendix 2-I

Sectional indicator

The 30-minute DEM's are distributed in groups of files that make up a 30- by 30-minute area of coverage representing the DEM for the east or west half of a 1:100,000-scale source map. The normal distribution group is four 15-minute files per 30-minute area. The quadrangle name field in the header record contains the name of the 1:100,000-scale source map. However, the pieces or sections into which each is divided are identified within the header type A record to the size and placement of each. In byte 138-140 each section is identified by a 3 character code

XNN where:

X is a single letter indicating size

F = 15-minute block

S = 7.5-minute block

NN is a two-digit number indicating the specific quad. Figure 2-I-1 and 2-I-2 illustrate this division with the sections labeled with the code that appears in bytes 138-140 of the header record.

F01 F02 F03 F04

F05 F06 F07 F08

Figure 2-I-1

A 1:100,000-scale quad divided into eight 15-minute quads, 4 per 30-minute area.

S01 S02 S03 S04 S05 S06 S07 S08

S09 S10 S11 S12 S13 S14 S15 S16

S17 S18 S19 S20 S21 S22 S23 S24

S25 S26 S27 S28 S29 S30 S31 S32

Figure 2-I-2

A 1:100,000-scale quad divided into 32 7.5-minute quads, 16 per 30-minute area.'

Specify the section number by entering a number from one to eight in the Section number (1-8) box. Specify the section number by entering a number from one to eight for a 15-minute block. Specify the section number by entering a number from one to 32 for a 7.5-minute block. Ignore the section number for “Other” block types.

USGS Digital Elevation Model .DEM Export Options Dialog